The invention relates to an annular rotor having a hollow shaft for an electric machine. The invention will be used in particular for very large electric machines such as, for example, gearless generators for wind-power plants.
As gearless wind-energy plants move to higher performance categories they are increasingly able to compete with geared plants. The rotor hub is linked directly to a synchronous generator in gearless wind-energy plants. The chief advantage of such a design is its much simpler structure requiring fewer rotating machine components compared with wind-power plants having a generator. Reduced maintenance costs and increased plant availability are the result.
In particular very large wind-power plants operate as a rule at very low speeds. Such plants must therefore in a gearless embodiment be fitted with very large and heavy generators. The diameter of these machines will then easily exceed the limit of 4 to 5 m.
Generators for gearless wind-power plants frequently include an annular rotor having a hollow shaft. Such an electric machine is known from, for instance, WO 2006/032969 A2. That publication discloses a rotor that is subdivided into a plurality of segments, with the segments having been pushed onto a rotor ring of the rotor.
Wind-power generators are becoming more and more difficult to install because of the increasing size perforce accompanying these plants higher output ratings. However, gearless turbines of wind-power or tidal power stations also pose major challenges in transportation and logistics terms.